Influences of DC bus voltage dynamics in modulation algorithm on power oscillations in PMSG-based wind farms

In the research of power oscillations caused by interaction between permanent magnetic synchronous generator (PMSG)-based wind farms and AC systems, influences of the machine side are usually ignored for simplification. This paper finds out that the indispensable condition for ignoring the machine side is the inclusion of DC bus voltage dynamics in modulation algorithm. Ignoring this condition could lead to inaccurate stability analysis results. Firstly, this paper constructs the small signal model and impedance model of the system when the modulation algorithm excludes and includes the DC bus voltage dynamics, which are both well-developed methods. Then the different influences of the machine side on the system stability with the two modulation algorithms are analyzed and explained theoretically. Thereby, the condition of ignoring the machine side in stability analysis is obtained. Eigenvalue analysis and time-domain simulation in a typical PMSG-based wind farm system demonstrate the theoretical analysis.